This invention relates generally to machines for forming, filling and sealing packages from an elongated thin flat strip of flexible packaging material, the strip of material being first formed to a depending upwardly open tubular configuration, sealed longitudinally at overlapped vertically extending edge portions, sealed transversely along horizontal lines spaced vertically along the tube, and filled from above with measured quantitites of product between successive transverse or end sealing operations. In advancing or drawing the packaging material downwardly through a tube former at the top of the machine, one conventional practice involves the use of end sealing jaws or bars movable in both horizontal and vertical planes. That is, the end sealing jaws are intermittently moved horizontally inwardly to engage and compress the tube and are then moved vertically downwardly to feed or draw the packaging material through the former. End sealing occurs during the feed operation. Subsequently, the end sealing jaws are moved horizontally outwardly to release the tube and are then returned vertically to their starting position.
Another known practice in advancing or feeding a strip of packaging material through a tube former involves the use of a vacuum feed belt mechanism. A pair of perforate endless belts are disposed respectively on opposite sides of the tube to engage and feed the same downwardly with gripping action provided by a reduced pressure or vacuum condition at openings in the belt. End sealing jaws in this arrangement may be stationary vertically but movable horizontally to intermittently engage, compress and transversely seal the tube between tube feed and product drop or fill operations. German Patent, Auslegeschrift No. 1,586,086, Mar. 23, 1972, discloses a vacuum belt tube feeder in a "tube type" vertical form, fill and seal packaging machine. That is, the machine includes a vertically extending tube within the tube of packaging material which serves to guide a tube of packaging material thereabout and through which measured quantities of product fall in filling the tube of material and packages formed therefrom. U.S. Pat. No. 4,043,098, entitled VERTICAL FORM, FILL AND SEAL PACKAGING MACHINE WITH IMPROVED BACK-UP BAR FOR LONGITUDINAL SEALING, dated Aug. 23, 1977, discloses a vacuum belt mechanism machines in a "tubeless" vertical form, fill and seal machine. In a "tubeless" arrangement, a short vertical tube may be provided within the tube former and the tube packaging material, but the tube terminates at its lower end above the vaccum feed belts. In the region of the feed belts, belt back-up means and side sealing back-up means are provided within the tube of packaging material but are of minimal cross section viewed vertically so as not to interfere with free product fall within the tube of packaging material.
In both of the foregoing arrangements, a relatively long "product drop" is encountered. That is, the distance through which charges of product must fall from the discharge end of the product dispensing means is quite substantial. With the vertically movable end sealer arrangement the necessary vertical or tube feeding travel of the end sealing jaws results in a substantial vertical distance through which the product must fall in the filling operation. Additionally, it will be noted that the portion of the tube immediately above the end sealer is maintained in tension and may be drawn into a relatively sharp or tight "V" configuration during downward movement of the end sealer jaws. Such a tube configuration is not conducive to a good filling operation nor is resulting stress on the tube of packaging material at the end sealing jaws conducive to good end sealing operation.
In the vacuum feed belt arrangement, belt and end sealer operation can be coordinated to provide for a relaxed condition of a tube of packaging material above the end sealer, a relatively loose "V" configuration or a "U" configuration with a slight bulge being provided, and this is conducive to a good filling operation. End sealing may also be efficiently accomplished in the absence of stress on the tube of material during sealing. The inner or operative runs of the vacuum belts, however, must extend through a substantial vertical distance in order to provide sufficient belt-tube contact area for good pure vacuum gripping operation and positive tube feeding action. Thus, some improvement over an end sealer feeding arrangement may be realized but a relatively long product drop is still encountered.
A relatively long product drop distance is generally acceptable for heavy product allowed to fall freely from a product dispensing means in measured quantities into a tube of packaging material. Such is not the case, however with relatively light product such as potato chips and other snack foods. With light product a condition known as product "string out" is encountered wherein air resistance may cause an upper portion of a mass of descending product to decelerate relative to the main body of the mass product. That is, a number of potato chips at the top of a mass of falling chips may tend to "string out" vertically above the main body of the mass as it falls into the tube of packaging material. Obviously, the time required for each filling operation may be significantly increased by product "string out," and this may result in turn in a severe limitation on the overall speed of operation of the machine and production rates will be detrimentally affected.
In addition to the foregoing, a "tubeless" type packaging machine is much to be preferred in handling lightweight product such as potato chips. Jamming of product may obviously occur within the stationary tube of a "tube type" machine. In a "tubeless" machine minimal interference with product fall is achieved with minimal cross sectional area of necessary back-up means within the tube. Further, timing of machine operation may be adjusted to provide for tube feed or downward tube movement assisting at least a portion of the filling operation. That is, without a tube in the feed zone, a mass of potato chips or the like can be engaged peripherally by a downwardly moving tube of packaging material in areas between the back-up means. Thus, a much improved filling operation with lightweight material can be achieved.
From the foregoing, it will be apparent that the efficient high speed handling of potato chips and other lightweight product is best accomplished in a vacuum form, fill and seal machine which is of the "tubeless" type and which provides for a minimum product drop distance.
It is a general object of the present invention to provide a "tubeless" vertical, form, fill and seal packaging machine which has the shortest possible "product drop distance" and which is therefore particularly well-suited to efficient high speed operation in the packaging of relatively lightweight product such as potato chips.
A further object of the invention resides in the provision of a tube feed means which occupies a minimum vertical space in the machine, which yet provides for positive and efficient feeding of a tube of packaging material and which also provides for a relaxed condition of the tube above the end sealer for efficient filling and end sealing.
A still further object of the invention resides in the provision of a packaging machine of the type mentioned wherein a combined vacuum-friction tube feeding action is employed to insure fast positive feeding operation in an extremely short vertical feed zone.
A still further object resides in the provision of a tube feed means of the combined vacuum-friction type wherein provision is made for enhanced vacuum gripping operation in the prevention of lateral vacuum loss between the edge portions of the feed belts and the tube of packaging material.